Fuel burner control system



Aug. 9, 138.

E. D. LILJA 2,326,199

FUEL BURNER CONTROL SYSTEM Original Filed May 11. 1936 T0 LINE INVENTOR E ga D. Lil/ 0 ATTORNEYS Patented Aug. 9, 1938 UNITED STATES FUEL BURNER CONTROL SYSTEM Edgar D. Lilja, Rockford, Ill., assignor to Howard D Colman, Rockford, Ill.

Application May 11, 1936, Serial No. 78,975 Renewed December 30, 193':

2 Claims. (01. 158-28) My invention relates to control systems for fuel burners and more particularly to such systems embodying electrical ignition means for igniting the fuel to initiate operation of the fuel 5 burner.

Difliculty has heretofore been encountered in the operation of fuel burners provided with such control systems since dangerous explosions are likely to occur if the operation of the ignition means is inadvertently delayed until .a substantial quantity offuel has been delivered to the burner. That is, if a spark of the proper intensity is produced immediately when the burner motor is started or before any substantial quantity of fuel has been discharged into the fire box, satisfactory ignition will take place. If, on the other hand, a spark of proper intensity is produced only after a comparatively large quantity of fuel has been supplied to the burner, there is danger of an explosion. q

The primary object of my invention'is to provide a control system for fuel burners including an improved detector arrangement operable in response to an electrical discharge of suflicient intensity to ignite the fuel and adapted to control the burner fuel supply mechanism in a manner such as to avoid the possibility of an explosion in case the igniter does not function properly.

More specifically, it is an object of my invention to provide an ignition detector arrangement for use in the control system described for fuel burners in which an oscillatory current is set up by the electrical discharge in the ignition means and is utilized to condition the fuel supply of the burner for operation, the oscillatory current being of a relatively high frequency as compared to the frequency of the current supplied to the ignition means.

40 Further objects and advantages of my invention will become apparent as the following description proceeds and the features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification.

For a better understanding of my invention, reference may be had to the accompanying drawing in which the single figure is a diagrammatic representation of a fuel burner control system embodying my invention and showing particularly the circuit connections therefor."

In the exemplary'form shown in the drawing, my invention is embodied in a control circuit adapted to control the operation of a conventional 5 liquid fuel burner I in accordance with the temperature requirements of a room or other compartment supplied with heat from the burner. The burner I0 includes an electric motor II which serves to drive a pump l2 that supplies 1 liquid fuel to a. burner nozzle l3.

It is desirable that some arrangement be provided for automatically igniting the fuel discharged from the nozzle l3 when operation of the burner is initiated. Accordingly, a pair of electrodes l4 are arranged in spaced relation ad- 10 jacent the open end of the nozzle. Ari electrical discharge is produced between the electrodes by a suitable step-up ignition transformer l5 having inductively coupled primary and secondarywindings. The electrodes M are connected across- 15 the secondary winding of the ignition transformer l5 by conductors IS. The primary winding of the transformer I5 is connected to a source of electrical energy through a control circuit hereinafter described, which is adapted to ef- 20 feet cyclic operation of the fuel burner.

'In accordance with my invention, I have provided an arrangement for controlling the fuel supply means of the burner Ill which is responsive to the passage of a substantially continuous 26 electric discharge between the electrodes llof sufficient intensity to ignite the fuel. This arrangement preferably includes an auxiliary circuit to which energy is transferred in response to changes in voltage or current at the electrodes 80 M, a capacitance and a coupling coil of low mutual inductance associated with the auxiliary circuit being utilized to render the auxiliary circuit resonant at a comparatively high frequency and thereby prevent the transfer of appreciable 35 energy to the auxiliary circuit at the frequency of the power supply to the ignition transformer I5. By comparatively high frequency is meant a frequency high as compared to the frequency of the power supply for the transformer I5; 40 Such a. capacitance or inductance renders the detector arrangement insensitive to the opencircuit voltage and short-circuit current of the ignition gap while rendering it sensitive to im-' pulses of energy transferred as a result of a dis- 45 charge of predetermined intensity between the electrodes. Thus, a circuit including a capacitance and an inductance may be associated with the electrodes in such manner that an oscillatory current is set up therein upon the passage 50 of an electrical discharge of predetermined intensity between the electrodes M. This oscillatory current may then be utilized to control the operation of the motor ll of the burner III.

In the construction illustrated, a condenser I1 is disposed within an air core inductance coil I8 and is connected in series relation therewith by conductor is. The coil I8 is wound on a cylindrical insulating core It. A second air core inductance coil 20 is arranged concentrically about the inductance coil l8 and is inductively coupled therewith. The coil 20 is wound on a cylindrical insulating core 20. The windings Ill and 20, and condenser l1 thus form a compact unitary structure. The series connected winding l8 and condenser l1 are connected in shunt relation with the electrodes [4 by conductors 2|. Consequently, upon the occurrence of a spark at the electrodes l4, a damped oscillatory current flows in the circuit including the condenser I1 and inductance coil I8. This current flowing through the inductance coil it induces a high frequency voltage in the secondary winding 26 which is utilized to control the operation of the fuel burner I! as is described below.

It is desirable that fuel should be supplied to the burner It) only in case a sustained electrical discharge of predetermined intensity is produced across the electrodes l4 as contrasted with a single unrepeated discharge or weak continuous discharge which would not insure proper ignition of the fuel subsequently supplied to the nozzle I3. Consequently, I prefer to utilize the voltage induced in the secondary winding 20 to operate what may conveniently be termed an integrating circult control device; that is, a circuit control device which is responsive to the integrated rather than the instantaneous value of an electrical characteristic such as voltage or current.

In the control circuit illustrated, an electrothermal relay 22 serves as the integrating circuit control device. The relay 22 includes a U-shaped conductor or wire 23 having its ends secured to the opposite sides of an insulating projection 24 on the base 25 and passing over a peripherally grooved insulating disk 25 also mounted on the base 25. The conductor 23 has a comparatively .high resistance as well as a high coefiicient of thermal expansion. The terminals of the secondary winding 20 are connected to the ends of the conductor 23 by conductors 21. Consequently, the voltage induced in the secondary winding 20 will cause a current to flow through the conductor 2t and heat the same. When a sustained electrical discharge of predetermined intensity sumcient to ignite the fuel passes between the electrodes l4, the integrated heating effect of the current flowing through the conductor 23 will result in a sufficient expansion of the conductor 22 to cause it to operate a circuit controlling device. The electro-thermal relay is preferably so proportioned as to effect fairly rapid actuation thereof when a discharge of the required intensity or ignition value is produced.

The circuit controlling elements of the electrothermal relay 22 include a pair of normally open contacts 2|. One of these contacts is mounted on the base 25 and the other is secured to'a movable supporting arm including a channelshaped outer link 25, which is pivotally connected by a pin ll to a second channel-shaped link II. The link II is in turn rigidly secured to the outer end of a flexible spring arm 32 fixed at its other end to a projection 33 on the base 25. The conductor 23 passes through an aperture 24 formed in a projection 35, which extends laterally from link 29 through the side of link 3|.

The parts of the relay are so arranged that the resilient arm 32 normally tends to swing the links 8| and 29 in a direction to close the contacts 28. The conductor 23 passing through the aperture 34 in the projection 25 is made short enough, however, so that the contacts 28 are normally maintained open, the arm 32 being flexed toward the conductor 23. It will thus be seen that when the conductor 23 is heated by the passage of a sustained current therethrough, its consequent elongation will permit the contacts 28 to be closed by the resilient arm 32.

Since accidental breakage of the conductor 22 would result in the same motion of the arm 32 as is caused by heating of the conductor, an arrangement has been provided to prevent sus tained closure of the contacts 28 in case of such breakage. This arrangement includes a pin it rigidly secured to the base 25 and spaced a sufficient lateral distance from the link 2! that it does not engage the same during the normal operation of the relay. Upon breakage of the conductor 23, however, the arm 32 and its attached links 3| and 29 swing in a clockwise di rection farther than during their normal movement and, consequently, the link 25 is brought into contact with the pin .36. As a result, the link 29 is swung about its pivot Ill, upon being pressed against the pin 35, so that the contacts 28 are maintained in open position.

Contacts 28 are closed momentarily during the abnormal motion of link 29, but not long enough to initiate operation of the burner.

I have shown, for purposes of illustration, a specific preferred form of burner control in connection with the improved ignition detecting arrangement described, but it should be understood that any desired main control may be used. In the specific arrangement illustrated, the control circuit is conditioned for operation by a main switch exemplified as a bimetallic thermostatic switch 31 which may be conveniently located within the chamber or room to be heated.

The exemplary control circuit is adapted to supply electrical energy to the ignition transformer I5 upon closure of contacts 35 of the thermostatic switch 31, when the temperature of the chamber in which the switch is located falls to a predetermined value. Thus, upon closure of the contacts 38, actuating winding 2! of an ignition control relay 4|! is energized by current supplied thereto from secondary winding 41 of a transformer '42.

Primary winding 43 of the transformer 42 is connected to a suitable source of alternating current 44, such as a household lighting system. through normally closed contacts 45 of a thermal safety switch 45. One terminal of the relay winding 39 is connected to the transformer 42; by a circuit including a conductor 41 extending from the transformer secondary winding 4i to the thermostatic switch 31, contacts 2!, conductor 48, normally closed contacts 45-40 and -52 of a combustion responsive switch mechanism It, conductor 54, heating coil 55 of the safety switch 46, and conductor 55. The other terminalof the relay winding 35 is connected to the second terminal of the power transformer secondary windingby a conductor 51. Consequently, upontransformer is permanently connected to one side 15 relay. Thus, upon closure of the contacts 58, the

.thermostatic switch is shunted out of the energizing circuit of the relay winding 39 by, conductors 64 and 65. v M

' Upon energization of the ignition transformer I5 described, an electric discharge is produced between the electrodes l4 and a high frequency voltage is'induced in the secondary winding 26 of the ignition detector. After the high frequency current has flowed through the conductor 23 of the electro-thermal relay 22 for a sufficient time, the conductor23 is elongated due to thermal expansion so as to permit the closure of contacts 28.

The contacts 28 are associated with the energizing circuit of the burner motor ii in such manner that the burner motor is conditioned for operation upon the closure of these contacts. Thus, the energizing circuit of actuating winding 66 of a motor control relay 6'! is completed upon closure of the contacts 28. 'Currentis supplied to the Winding 66 from one terminal of the secondary winding 4| of the transformer 42 through conductor 41, conductor 68, contacts 28 and conductor 69. The other terminal of the secondary winding 4! of the transformer 42 is permanently connected to the relay winding 66 through conductors 51 and i6.

Energization of the windihg 66 causes the closure of contacts H and 12 of the motor control relay 61, which in turn results in the energization of burner motor ll. Thus, one terminal of the motor H is permanently connected to one side of the supply line 44 through conductor 66, while the otherterminal of the motor II is connected to the other side of the supply line 44 through conductor l3, contacts H, conductors l4 and 62 and contacts 45 of safety switch 46. The motor it is thus set in operation and fuel is supplied under pressure to the nozzle l3 where it is ignited by the electrical discharge between the electrodes M.

It will be seen that if a sustained electrical discharge of predetermined strength is not had at the electrodes i4, either because of short circuiting of the gap or failure of the gap voltage due to any other cause, the conductor 23 will not be heated suificiently to permit closure of the contacts 28. In such case, the motor control relay M will not be energized and no fuel will be sup plied to the nozzle 63. Hence, with the circuit arrangement described, the existence of a suitable ignition discharge at the electrodes I4 is a positive prerequisite to the operation of the burner fuel supply means.

If satisfactory operation of the ignition means is not had within a predetermined time, contacts 45 of the safety switch 46 are opened, disabling the entire control system as is hereinafter described. The safety switch 46 can only be reclosed by subsequent manual operation so that the attention of the operator is drawn to the failure of the ignition apparatus to operate properly.

The combustion responsive switch 53 is adapted to remove the motor control relay 6! from the control of the ignition detecting device and place it under the control of the main thermostatic switch 31 as well as subsequently to deenergize the ignition transformer IS in the event of successful ignition of the fuel. In order to eflect this operation, the mechanism 53 is of the usual thermostatic type comprising a bimetallic thermostatic member 15 located within the furnace flue or stack 16, which is heated by the products of combustion leaving the furnace. When the thermostatic element I5 becomes heated, it rotates an actuating member H in a counterclockwise direction, thus opening the contacts 43 and 50. Upon further rotation of the actuating member I1, contacts 18 and 19 are closed, thus completing an energizing circuit for the actuating winding 66 of the motor control relay 6'! independent of the electro-thermal relay contacts 28. This circuit extends from the secondary winding of the transformer 42 through conductor 41, contacts 38 of the main switch 31, conductor 48, contacts 18-19, conductor 80, protective resistance 8|, conductor 62, contacts 12 of the motor control relay 61, and conductor 83 to one terminal of winding 66. The other terminal of the relay winding 66 is, of course, permanently connected to the transformer 42 through conductors 5i and 16.

Upon further rotation of the actuating member ll of stack switch 53, contacts 5 l-52 are opened, breaking the energizing circuit of the actuating winding 39 of the ignition control relay 48. The winding 39 is thus deenergized permitting the contacts 58 and 59 to open, which in turn breaks the energizing circuit of the ignition transformer 15. The electrical discharge between the electrodes I4 is thus terminated when the heating of the switch 53 indicates that satisfactory ignition of the fuel has been effected.

From the foregoing,'it will be seen that the energizing circuit of the motor control relay 61 is in this part of the cycle, controlled by the contacts 38 of the main thermostatic switch 31. After the fuel burner has been in operation for a sufficient length of time to raise the chamber temperature above the control point of the thermostatic switch 31, the contacts 38 are again opened. The energizing circuit for actuating coil 66 of the motor control relay 6'! is thus broken,

I thereby opening contacts II and i2 and in turn deenergizing the burner motor II to shut off the burner. The cycle described above is repeated at intervals in order to maintain the temperature of the chamber being heated within predetermined temperature limits.

It will be noted that the heating coil of the safety switch 46 is energized immediately upon the initiation of the control cycle by the main control thermostatic switch 31. This heating coil 55 is so positioned with respect to a bimetallic thermostatic latch 84 that the latter will be heated so as to permit the contacts 45 of the safety switch to open after a predetermined length of time. Thus, if satisfactory ignition is not had within a predetermined interval of time, the contacts 45 of the safety switch 46 will be opened, deenergizing the actuating winding 39 of the ignition control relay 40 and rendering the apparatus inoperative until the safety switch 46 is manually reset. If satisfactory ignition of the fuel is effected, however, the energizing circuit for the heating coil 55 of the safety switch is opened by contacts 5| and 52 of the combustion responsive switch 53.

It will thus be seen that I have provided a compact and simple arrangement for positively controlling the fuel supply of a fuel burner in such manner that no fuel will be supplied to the burner until satisfactory operation of the ignition means thereof is had. Moreover, the circult arrangement of the improved ignition detector means is such that normal cyclic operation of the burner under control of a main thermostatic switch is permitted.

Although I have shown a particular embodiment of my invention in connection with a liquid fuel type burner, I do not intend to limit the invention to the particular construction shown and described but aim to cover all modifications falling within the spirit and scope of the invention ass-expressed in the appended claims.

I claim as my invention:

1. A control system for a fuel burner comprising, in combination, electric motor driven means for supplying fuel to the burner, a supply circuit for said means, a spark igniter circuit including spark electrodes associated with said fuel supply means and a low frequency current supply for said electrodes, 9. high frequency circuit associated with said ignition circuit and energized to high frequency oscillations solely by normal spark at said electrodes, a thermally operated time delay switch having the heating element thereof energized solely by said high frequency circuit, said time delay switch having its contacts arranged to control said first-named circuit whereby to initiate fuel supply to the burner only after a sustained normal spark has occurred at said electrodes.

2. A control system for a fuel burner comprising, in combination, means for supplying fuel to the burner, a spark igniter circuit including spark electrodes associated with said fuel supply means-and adapted to be connected to a low frequency current supply source, a high frequency circuit associated with said-ignition circuit and energized by high frequency oscillations solely by normal sparking between said electrodes, and control means responsive only to a sustained ener gization of said high frequency circuit for a predetermined time interval for governing said fuel supply means whereby to initiate fuel supply to the burneronly after a sustained normal spark has occurred at said electrodes.

EDGAR D. LILJA. 

